A. Field of the Invention
This invention relates to the technology presently known as Internet telephony (sometimes referred to in the art as IP Telephony, where IP stands for Internet Protocol), in which signals from a caller station, such as a telephone, fax machine, modem, or video device, are transmitted, in the form of digital data packets, across a digital data network to a callee station. More particularly, this invention relates to a system and a method for Internet telephony that uses network address translation to translate the source and destination addresses of the digital data packets as they are transmitted from the address space of one network to the address space of another network.
B. Description of Related Art
Internet telephony is becoming an increasingly attractive alternative to the conventional public switched telephone network (PSTN) for long distance telephone calls because of its much lower cost and enhanced flexibility. To make a long distance telephone call using Internet telephony, a caller typically need only make a local telephone call to a local Internet telephony service provider. The Internet service provider then routes the telephone call to the Internet, often by using a gateway or terminal functioning in accordance with the H.323 and H.225 ITU-T standards. The H.323 and H.225 ITU-T standards are incorporated herein by reference. Another protocol that has been proposed is the xe2x80x9cSession Initiation Protocolxe2x80x9d (SIP). The most recent version of SIP is described in the Network Working Group""s Request for Comments 2543 (March 1999), which is incorporated herein by reference.
Once the telephone call is routed to the Internet, its transmission is, for all practical purposes, free, regardless of its destination. Accordingly, in contrast to long distance service on the PSTN, which may charge users 10 to 30 cents per minute for domestic calls and considerably more for international calls, the cost of a long distance call using Internet telephony is potentially the cost of two local telephone calls (one at the calling end and one at the receiving end).
One problem with this conventional implementation of Internet telephony, however, is that it is not as user-friendly as the PSTN. Specifically, when a user desires to route a telephone call using conventional Internet telephony, the user typically must call a special telephone number, i.e., the telephone number of the Internet telephony service provider, and then dial the telephone number of the desired destination. In contrast, to use the PSTN, the user need only dial the telephone number of the desired destination.
One possible solution to this problem would be to bypass the PSTN entirely and provide telephones with direct Internet access. However, providing an Internet address for each telephone that uses Internet telephony may not be practical because of the increasingly limited number of available Internet addresses.
Finally, conventional Internet telephony has problems with privacy and security. The privacy concern relates to the extent to which the caller and callee can remain anonymous. The security concern relates to how easily an unauthorized party can gain access to the system, such as to make long distance calls without paying for them.
In a first principal aspect, a system is provided for routing a call between a caller station, connected to an edge network, and a callee station, accessible via an intermediate network. The callee station is associated with a callee station number. A router, connecting the edge network to the intermediate network, initiates the call in response to a setup message that includes the callee station number. During the call, the router performs network address translation on the caller signal from the caller station in order to transmit the signal from the edge network to the intermediate network. Similarly, the router performs network address translation on the callee signal from the callee station in order to transmit the signal from the intermediate network to the edge network.
In a second principal aspect, a system is provided for routing a call between a caller station, connected to an edge network, and a callee station, accessible via an intermediate network. The callee station is associated with a callee station number. A routing means initiates the call in response to a setup message that includes the callee station number. During the call, the routing means performs network address translation on the caller signal from the caller station in order to transmit the signal from the edge network to the intermediate network. Similarly, the routing performs network address translation on the callee signal from the callee station in order to transmit the signal from the intermediate network to the edge network. A gatekeeper means controls the routing means.
In a third principal aspect, an improvement is provided to a communication system for routing a call between a caller station and a callee station. The communication system includes the caller station, connected to an edge network, and the callee station, accessible via an intermediate network. The callee station is associated with a callee station number. The improvement comprises a router, connecting the edge network to the intermediate network that initiates the call in response to a setup message that includes the callee station number. During the call, the router performs network address translation on the caller signal from the caller station in order to transmit the signal from the edge network to the intermediate network. Similarly, the router performs network address translation on the callee signal from the callee station in order to transmit the signal from the intermediate network to the edge network.
In a fourth principal aspect, a method is provided for setting up a call over an intermediate network from a caller station, connected to an edge network, to a callee station, accessible via the intermediate network. The callee station is associated with a callee station number. A setup message, which includes the callee station number, is received from the edge network. A proxy public caller address is then allocated to identify the caller station on the intermediate network, and a proxy private callee address is allocated to identify the callee station on the edge network.
In a fifth principal aspect, a method is provided for communicating over an intermediate network between a caller station, connected to an edge network, and a callee station, accessible via the intermediate network. A caller signal comprising first caller data packets is received from the edge network. Network address translation is performed in the first caller data packets to provide second caller data packets that are then transmitted over the intermediate network.
In a sixth principal aspect, a method is provided for registering a caller station with a server. The server receives a registration message that includes a caller station number, a caller address, as well as the public addresses of the router and gatekeeper associated with the caller station. The server then stores the information in a database.
In a seventh principal aspect, a system is provided for setting up a call between a caller station, connected to an edge network, and a callee station accessible via the intermediate network, where the intermediate network is connected to the edge network by a router. The system comprises a gatekeeper, connected to the intermediate network, that controls when the router allocates a proxy public caller address to identify the caller station on the intermediate network and when the router allocates a proxy private callee address to identify the callee station on the edge network.
In general, a preferred embodiment of the present invention provides a system and method for Internet telephony that allows for long distance calls at a lower cost than the PSTN while still being as easy to use as the PSTN. Specifically, the user is able to route a call by dialing only the telephone number of the desired destination, without first calling a special telephone number.
The preferred embodiment of the present invention, though independent of the PSTN altogether, substantially conserves Internet address space by using network address translation. In particular, a caller station has a fixed caller address on a first edge network and a callee station has a fixed callee address on a second edge network. The caller and callee stations are allocated Internet addresses only when a call is being set up between them. Network address translation is used to transmit the signals between the Internet and the first edge network and is also used to transmit signals between the Internet and the second edge network. Moreover, once the call is completed, the Internet addresses will be available for other stations to use.
Privacy and security concerns are also addressed by the preferred embodiment of the present invention. Through the use of proxy addresses, one side of the call does not have access to the private addresses of the other side. This provides an important measure of privacy. Security is also enhanced because several different components, namely two routers, two gatekeepers, and a back end server, must all work together to set up a call. The distributed nature of the system makes unauthorized access much more difficult.